No, and it's not to do with people turning away from alching. Or if it is it will make a marginal difference. Considering that pking as come back, many more nature runes are being bought by pkers for when they hybrid norm magics (using entangle). Besides, the population of F2p is colossal, and the most effective way to train magic there is still alching.

It's to do with a new(ish) flawless graahk script that has been released for like $4. Most graahkers are using this bot and it's as fast if not faster than crafting nats manually. It's extremely hard to detect and so they're run for 10/15 hours at a time, racking in tens of thousands of nature runes. This sudden influx of supply has forced the prices down considerably. I doubt nature runes will ever reach 300gp again.

Besides, the population of F2p is colossal, and the most effective way to train magic there is still alching.

Superheating is faster xp, with less lost cash in f2p..

Except Superheat also uses natures so it doesn't really make a difference. But yeah, way too many people crafting (or botting) natures nowadays, don't see it changing anytime soon, so natures will probably stay pretty steady (if not drop).

No, they won't rise much. You have to realise that the supply:demand ratio won't change drastically because looking at this in the simplest form:
People will be training Rc on Nats during DXPW
Others will be training Mage with Nat-Spells during DXPW.